Determining endpoint in a substrate process

ABSTRACT

An endpoint detection method for detecting an endpoint of a process comprises determining a reflectance spectrum of light reflected from a substrate, the light having a wavelength, processing the substrate while light having the wavelength is reflected from the substrate, detecting light having the wavelength after the light is reflected from the substrate, generating a signal trace of the intensity of the reflected light and normalizing the signal trace with the reflectance spectrum of the light. The normalized signal trace can then be evaluated to determine an endpoint of the process.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.12/898,672, filed on Oct. 5, 2010, which is a continuation of U.S.application Ser. No. 12/688,840, filed on Jan. 15, 2010, which is acontinuation of U.S. application Ser. No. 11/953,853, filed on Dec. 10,2007, which is a divisional application of U.S. application Ser. No.10/286,402, filed on Nov. 1, 2002, all of which are incorporated byreference herein in their entireties.

BACKGROUND

The present invention relates to the detection of an endpoint in theetching of a substrate.

In the processing of a substrate to fabricate electronic devices, suchas integrated circuits and displays, etching processes are carried outto etch materials on the substrate to form patterned features that formcomponents of the electronic devices. For example, the patternedfeatures may comprise gates, vias, contact holes, or interconnect lines.Typically, a patterned mask of etch-resistant features comprising resistor hard-mask materials is formed on the substrate, and exposed areas ofthe substrate between the etch-resistant features are etched to form thepatterned features.

During the etching process, an endpoint determination method is used toevaluate and control etching progress through the substrate, such as tostop or change etching parameters at a predetermined etch depth. Ininterferometric endpoint determination methods, as illustrated in FIG. 1(prior art), light beams 76 a,b are directed onto the substrate 10 andthe beams are reflected from the substrate 10 to form reflected lightbeams 78 a,b. Constructive and destructive interference of the reflectedlight beams 78 a,b modulate the total or summed reflected light 78 overtime to generate interference fringes having intensity maxima andminima. The reflected light 78 is detected by a detector that generatesa reflection signal, and the reflection signal is monitored to determinean endpoint of the etching process. The reflection signal exhibitsmaxima and minima peaks that correspond to interference fringes thatarise from primary reflections 78 a from the surface of the etch layer22 and secondary surface reflections 78 b from the surface of the maskfeatures 24, as well as from other reflections from internal interfacesbetween layers of the substrate 10. By counting these interferencefringes, it can be determined when an etching process endpoint has beenreached, such as a particular etch depth or etch rate, that occurs aftera predetermined number of fringes are counted.

However, the effective signal-to-noise ratio of the interference fringesof the reflected light 78 is relatively low because the intensity of theinterference signal is also affected by the internal reflections thatarise from interfaces within the substrate 10. For example, a portion 76b of the light beam 76 that is incident on the mask features 24 is alsopartially transmitted to the interface 26 between the mask features 24and the etch layer 22. The reflection 78 c of the light beam 78 from theinterface beneath the mask features 24 undesirably interferes with thesurface reflections 78 a,b to reduce the overall strength or intensityof the reflected light beam 78. This reduction of the reflected lightbeam intensity hinders endpoint detection by decreasing the effectivesignal-to-noise ratio of the interference fringes.

As semiconductor devices are fabricated to have increasingly smallerdimensions, it is desirable to detect endpoint with better precision, tostop or change processing when the desired small dimension is reached.However, interface reflections 78 c from below the mask features 24effectively limit the precision and accuracy of endpoint detection byadding noise to the reflection signal. While this noise can be partiallyremoved using filters such as bandpass filters, the filters increase thecomplexity of the endpoint detection system and often do not reduce thenoise to a sufficiently low level. Noise levels are particularlydeleterious when etching devices having shallower or more precisedepths, or when etching a thin layer on the substrate and stop etchingin due time without etching through the thin layer. layer. Accordingly,it is desirable to interferometrically determine the endpoint duringsubstrate processing with higher precision and better signal to noiseratio.

SUMMARY

A method of processing a substrate in a process zone is provided. Areflectance spectrum is determined from light reflected from asubstrate, the light having a wavelength. The substrate is processed byexposing the substrate to an energized gas in the process zone whilelight having the wavelength is reflected from the substrate. Lighthaving the wavelength after the light is reflected from the substrate isdetected and a signal trace of the intensity of the reflected light isgenerated. The signal trace is then normalized with the reflectancespectrum of the light and evaluated to determine an endpoint of theprocess.

In another method, a substrate is processed comprising an overlyingmaterial and an underlying material below the overlying material. Areflectance spectrum of light reflected from the underlying material ofthe substrate is determined when it is substantially absent thepatterned overlying material. The substrate is processed having theoverlying material and the underlying material, by exposing thesubstrate to an energized gas in the process zone while light having thewavelength is reflected from the substrate. Light having the wavelengthis detected after the light is reflected from the substrate, and asignal trace of the intensity of the reflected light is generated. Thesignal trace is normalized with the reflectance spectrum of the lightfrom the underlying material. The normalized signal trace is thenevaluated to determine an endpoint of the process.

DRAWINGS

These features, aspects, and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings which illustrate examples ofthe invention. However, it is to be understood that each of the featurescan be used in the invention in general, not merely in the context ofthe particular drawings, and the invention includes any combination ofthese features, where:

FIG. 1 (Prior Art) is a schematic cross-sectional side view of asubstrate from which a light beam is reflected to determine an endpointof etching of the substrate according to a conventional method;

FIG. 2 is a schematic cross-sectional side view of a substrate fromwhich a light beam is reflected to determine an endpoint of etching ofthe substrate according to an embodiment of the present invention;

FIG. 3 is a plot of reflected light intensity signals over time and fordifferent mask thicknesses;

FIG. 4 is a plot of reflected light intensity signals for differentwavelengths of light and different mask thicknesses;

FIG. 5 is a plot of desirable wavelength of light as a function of thethickness of the mask on the substrate from which the light having thewavelength is reflected;

FIG. 6 is a flowchart of process steps used to etch the substrate,detect an etching endpoint, and change the etching process;

FIG. 7 is a schematic sectional side view of a substrate processingapparatus and endpoint detection system according to the presentinvention; and

FIG. 8 is a schematic diagram of a controller of the substrateprocessing apparatus of FIG. 7.

DESCRIPTION

An endpoint detection system is useful in the fabrication of integratedcircuits on substrates, and is particularly useful in the etching ofsemiconductor, dielectric, or conductor materials of the substrate.Semiconductor and dielectric materials are often layered on one anotherand make it difficult, for example, to etch through a thick overlyingsemiconductor material while still stopping the etching process withoutetching through a thin underlying dielectric material. The dielectricmaterials may include, for example, nitrides, silicon oxide, silicondioxide, or low-k dielectrics; and the semiconductor materials mayinclude, for example, polysilicon or silicon. However, the endpointdetection can be used in the etching of other materials such asconductors, or in deposition processes, such as chemical vapordeposition (CVD) and physical vapor deposition (PVD) processes.

FIG. 2 illustrates an exemplary embodiment of a substrate 110 that canbe etched using the present process and that is not intended to belimiting. The substrate 110 comprises a mask 115 of patterned features162 comprising photoresist and/or hard mask, such as silicon oxide orsilicon nitride, that are formed by lithographic methods. In oneembodiment, the mask 115 comprises a nitride, such as silicon nitride.Alternatively, the mask 115 may comprise photoresist. Between the maskfeatures 162 are exposed areas 127 revealing the underlying materials ofthe substrate 110 that are open and exposed for etching. At the exposedareas 127, which are below the surface of the mask 115, the substrate110 comprises an etch material 130 that is to be etched, and anunderlying material 122 below the etch material 130. For example, theetch material 130 may be a semiconductor material such as polysilicon.An exemplary underlying material 122 comprises a thin silicon dioxidematerial, such as having a thickness of from about 10 to about 300Δ.

An example of an endpoint detection method for substrate etching willnow be described. In this process, the etch material 130 is etched andthe endpoint of the etching process is detected with high accuracy andprecision, thus avoiding undesirable etching or damaging of theunderlying material 122. As illustrated in FIG. 2, light 176 having aselected wavelength that is directed on the substrate 110 during theetching process. The intensity of the reflected light 178 is measured.The various reflected light beams 178 a-c of the incident light beams176 a,b constructively or destructively interfere with each other toproduce a net reflected light 178 with a rapidly modulated intensity asetching progresses, and the modulated intensity is monitored todetermine the occurrence of the endpoint.

A light wavelength selector 179 determines a wavelength of the light 176to locally maximize the intensity of the reflected light 178 at aninitial time point of the etching process. This intensity of thereflected light 178 has an approximate maximum at this determinedwavelength within a neighborhood of wavelengths. Wavelengths neighboringthe determined wavelength produce lower intensities than does thedetermined wavelength. This wavelength is selected to cause theinterference between the secondary surface reflection 178 b and theinterface reflection 178 c to be substantially constructive at theinitial time point at the beginning of an etch process stage, such asbefore etching or before one etching stage of a multi-stage etchingprocess. For example, a wavelength may be selected such that theadditional distance of the path of the interface reflection 178 cthrough the mask 115, in comparison to the path of the secondary surfacereflection 178 b, is approximately an integral multiple of the selectedwavelength to cause the secondary surface reflection 178 b and interfacereflection 178 c to be substantially in phase when they emerge from thesubstrate 110. Constructive interference occurs between the secondarysurface reflection 178 b and the interface reflection 178 c becausethese secondary surface and interface reflections 178 b,c are in phasewhen they interfere, and thus the intensities of the secondary surfaceand interface reflections 178 b,c sum to provide light 178 having ahigher intensity. In one version, when a wavelength provides a localmaximum of reflected intensity, one or more harmonics of that wavelength(integral multiples of the corresponding frequency) also provide localmaxima of the reflected intensity. Factors that can be considered asconstraints as constraints on the determined wavelength include theabsorption spectrum of the mask material. For example, a wavelength maybe selected that is not overly absorbed by the mask material even ifthat wavelength would otherwise provide good constructive interference.The wavelength may also be such that the mask, in its thickness appliedon the substrate 110, is permeable to light having the wavelength.Additionally, a wavelength is selected that provides goodinterferometric fringes when reflected from the substrate 110 beingetched because its magnitude is adapted to the lateral and verticaldimensions of the features of the substrate 110. For this embodiment,the selected wavelength is from about 220 to about 300 nm.

The wavelength of the incident light 176 may be scanned through asequence of successive wavelengths by the light wavelength selector 179,as shown in FIG. 7, to locate a suitable wavelength. The lightwavelength selector 179 changes a wavelength of a light reflected fromthe substrate 110 until a local maximum of an intensity of the lightreflected from the substrate is detected. For example, the wavelengthmay be scanned by reflecting the incident light 176 from a diffractiongrating 92 while rotating the diffraction grating 92. The diffractiongrating 92 can be rotated by a stepper motor 94 attached to thediffraction grating 92 along an axis that is non-orthogonal to a surfaceplane of the diffraction grating 92. When the diffraction grating 92 isrotated along this axis, light 176 having a different wavelength isdirected towards the substrate 110. Instead of a diffraction grating 92,the wavelength separation device may also be a prism or a selectivelytransparent medium, such as a wavelength filter.

Referring to FIG. 4, the wavelength where the intensity of the reflectedlight 178 is at a local maximum 213, the wave interference between thesecondary surface reflection 178 b from the top surface 125 of the mask115 and the interface reflection 178 c from the interface 126 below themask 115 is constructive rather than destructive. This arises becausethe secondary surface reflection 178 b and the interface reflection 178c, as is shown in FIG. 2, are in phase at an initial time point in theetching process, to cause constructive interference. In contrast, in theconventional method illustrated in FIG. 1, secondary surface andinterface reflections 78 b,c are out of phase at the initial time pointin the etching process, and result in non-constructive or at leastpartially destructive interference. Selection of the in-phase wavelengthprevents the secondary reflection 178 c coming from the interface 126below the mask 115 from substantially decreasing the value of theintensity of the reflected light 178. By maintaining a strongerintensity of the reflected light 178, changes in the intensity due tochanges in the etch depth are more pronounced and evident, and theprecision of the endpoint detection is thus improved.

An exemplary embodiment of a plot of intensity signals 209 over time asgenerated by a light detector 180 that receives the reflected light 178,which represent intensities of the reflected light 178, is shown in FIG.3. In each plot, the mutual interference between the surface reflections178 a,b of the reflected light 178 causes the intensity signal 209 todrop and then oscillate. This interference also includes the effect ofthe interface reflection 178 c from below the mask 115. However, sincethe mask 115 is substantially resistant to etching, and thus the maskthickness is substantially constant, the interference fringes of theoscillating signal evidence the phase shift between the secondarysurface reflection 178 b and the interface reflection 178 c, andindicate the change in etch depth. As a result, the net interferencesignal arising from etching of the exposed material, i.e., that occursfrom the changing path length between the light reflected from theetched surface of the substrate and that reflected from the mask surfaceand interface, is maximized. This improves the signal to noise ratio ofthe relevant portion of the endpoint signal.

In this figure, the reflected light intensity signals 209 over time, arefor an incident light beam 176 having a wavelength of 235 nm fromsubstrates 110 having silicon nitride masks 115 of differentthicknesses. The intensity signals 209 vary significantly depending onthe different mask thicknesses. A first curve 209 a represents theintensity signal 209 for a mask 115 having a thickness of 162 nm. Asecond curve 209 b corresponds to 153 nm; a third curve 209 ccorresponds to 144 nm; a fourth curve 209 d corresponds to 136 nm; afifth curve 209 e corresponds to 131 nm; and a sixth curve 209 fcorresponds to 121 nm. As shown by the significant differences andspacings between these curves 209 a-f, the thickness of the mask 115 hasa substantial effect on the intensity signal 209 of the reflected light178. For example, in this embodiment the 162 nm wavelength selectionresults in more pronounced interferometric fringes than the otherwavelength selections, and the 121 nm results in less pronouncedinterferometric fringes than the other wavelength selections. In betweenthese two values is a continuum of the degree to which the surfacereflection 178 b and interface reflection 178 c are destructivelyinterfering, the 162 nm wavelength selection resulting in substantiallyconstructive interference, and the 121 nm wavelength selection resultingin substantially destructive interference.

FIG. 4 is an empirically derived plot showing reflected light intensitysignals 209 as a function of the wavelength of the light, fromsubstrates 110 having silicon nitride masks 115 of differentthicknesses. A first curve 211 a represents the reflected intensitysignal for a mask 115 having a thickness of 164 nm. A second curve 211 brepresents the intensity signal for a mask 115 having a thickness of 153nm. And a third curve 211 c represents the intensity signal for a mask115 having a thickness of 136 nm. As shown in the Figure, the localmaxima 213 have different wavelengths and magnitudes at the differentmask thicknesses.

FIG. 5 is an empirical plot showing the change in desirable wavelength(nm) as a function of thickness (nm) of the mask 115. The desirablewavelength increases with increasing mask thickness. In this example,the desirable wavelength changes approximately linearly with the changein mask thickness. This empirically derived relationship between thedesirable wavelength and the mask thickness can be used to calculate byinterpolation, a desirable wavelength to be selected when the thicknessof the mask 115 is known or measured immediately prior to substrateetching, or determined at some initial etching time point.

From the intensity signal traces, the endpoint is typically detected bycounting a number of interference fringes in the intensity signal 210 ofthe reflected light 178, the interference fringes being periodic pointsin the intensity signal 210, such as local minima or maxima where thederivative of the signal is approximately zero. For example, theendpoint may be detected by counting a sequence of maxima, oralternatively by counting a sequence of minima. Fractional fringes canbe be counted according to the estimated time until the next fringebased on the shape of the signal waveform. Once a predetermined numberof interference fringes are counted, the etching endpoint is determinedto have occurred or be near. Alternatively, the endpoint may be detectedby comparing the intensity signal 210 of the reflected light 178 to anexpected intensity pattern.

The etch depth (d) may be calculated from the interference signal traceusing the following equation:

$d = \frac{f\; \lambda}{2\; n}$

where f is the number of interference fringes counted, λ is thewavelength, and n is the relative refractive index of the etch material130. For example, for a given etch depth (d), an expected number ofinterference fringes (f) can be calculated. For a desired etch depth,the intensity signal 210 is monitored and the interferences fringes arecounted until >f=fringes have been detected, at which time the etchingprocess is determined to have reached its endpoint.

The wavelength of light at which the local intensity of the signal traceis maximized can be selected by measurement or calculation. For example,the reflection and absorption characteristics of different wavelengthsof light reflected from a particular substrate 110 or mask/substratecombination may be determined early in the substrate processing, at aninitial time point before a particular etching process stage is started,by a calibration step conducted at the commencement of etching or beforethe interference fringes are obtained in the reflected signal trace. Forexample, if the substrate 110 comprises a patterned overlying materialand an underlying material, it may be desirable to know the reflectionand absorption characteristics of a similar substrate 110 that comprisesthe underlying material, but substantially absent the patternedoverlying material. For example, in one embodiment the overlyingmaterial comprises oxide and the underlying material comprises silicon.In one version, a broadband spectrum of light, such as a broadband flashof light, is directed at the substrate 110. Alternatively, a sequence ofwavelengths of light may be directed at the substrate 110. Light that isreflected from the substrate 110 is detected to determine a reflectancespectrum representing the the absorption and reflection characteristicsof a number of different wavelengths in relation to the particular typeof the substrate 110. This pre-etch stage calibration step generates areflectance “snapshot” of reflected intensity signals for a range ofultraviolet wavelengths of light 176 projected on the substrate 110.Exemplary embodiments of reflectance spectra are shown in FIG. 4.

This reflectance snapshot can then be used to normalize the intensitysignal 210 of the reflected light 178. For example, the intensity of thesignal trace at the wavelength of the light 178 can be normalized by theintensity of the reflectance spectrum at substantially the samewavelength. The normalization removes distortion of the intensity signal210 that is due to the reflection/absorption characteristics of thesubstrate 110 and the initial emission characteristics of the light 176from a light source 66.

In another embodiment, the desirable wavelength of the light 176 iscalculated from the reflectance spectrum of the substrate 110 and thethickness of the mask 115. The thickness of the mask 115 may bedetermined before the counting of the interference fringes by using aseparate interferometric method or with a profilometer. A wavelengththat results in constructive interference between the secondary surfacereflection 178 b and the interface reflection 178 c from the substrate110 can be calculated from the incidence angle of the light 176 onto thesurface of the substrate 110 and the thickness of the mask 115. Thecalculated wavelength of light that provides a local maximum ofintensity when light having the wavelength is reflected from thesubstrate. The wavelength is one for which the additional distance froma detection point, of a path of light that passes through the thicknessof the mask 115 and is reflected from the interface between the mask 115and the substrate 110, in comparison to a path of light that isreflected from the surface of the mask 115, is approximately an integralmultiple of the wavelength.

The etching and endpoint detection method of the present invention cansignificantly improve substrate yields by improving the precision ofendpoint detection as a function of time, thereby reducing undesirableetching or other damage of the material 122 underlying the etch material130. For example, the underlying material underlying material 122 may bea thin gate oxide layer during etching of a polysilicon etch material130. By stopping the etching process before the underlying material 122is damaged by the etching process, the present endpoint detection methodprovides higher yields and better quality of integrated circuits. Byselecting the wavelength of the substrate-incident light 176 to locallymaximize the intensity signal 210 at an initial time point of theetching process, destructive interference due to the interfacereflection 178 c from the interface below the mask 178 is decreasedthroughout the subsequent etching process, thus improving the precisionof the endpoint detection. In one embodiment, a minimum detectabletrench depth of less than about 200 nm can be achieved with endpointdetection at the selected wavelengths. For example, the endpointdetection can even detect etch depths of less than about 140 nm, andeven less than about 115 nm.

In the process of etching and endpoint detection, as represented by theflowchart of FIG. 6, the thickness of the etch material 130 iscontinuously measured in situ during an actual etching process. Whenetching is near completion, such as with about 300Δ of the etch material130 remaining on the substrate 110, the etching process is stopped orfirst process conditions are changed to second process conditions toprovide more controllable etch rates. For example, the second processconditions can provide slower and more controlled etching of the etchmaterial 130, and increase etching selectivity ratio for etching of theetch material 130 relative to underlying material 122. The etch processconditions can be changed by altering gas composition, substratetemperature, or gas energizing levels. For example, an etch rate can belowered by changing the composition of the etchant gas, such as removingaggressive etchant gases, lowering RF bias power levels, and loweringthe substrate temperature.

To controllably change process conditions after a given thickness of theetch material 130 is reached, the endpoint detection method is used todetect the thickness of the etch material 130 and feedback theinformation to a controller to change process conditions to provideparticular etch rates or etching selectivity ratios. The endpointdetection method can be used to detect the moment at which most of theetch material 130 is etched so that the first process conditions can bechanged to changed to less aggressive second process conditions, or viceversa, to obtain the desired change in etch rate, etching selectivityratio, or a change in any other property of the etching process, forexample, higher/lower etch rates or etching of the underlying material122 having a different composition. For example, the endpoint detectionmethod can be used to stop the etching process after a first highlyaggressive etching step, which provides high etch rates due to thepresence of a fluorinated gas in the etchant gas, to determine thestarting point for a second and less reactive etching step, which usesan etchant gas that is substantially absent the fluorinated gas to etchthe remaining etch material 130 at a slower etch rate to obtain a morecontrolled etching process.

The substrate 110 is etched in a substrate processing apparatus 40, suchas the embodiment schematically illustrated in FIG. 7, available fromApplied Materials Inc., Santa Clara, Calif. The apparatus 40 comprises aprocess chamber 42 having a process zone 44 for processing the substrate110, and a support 46 such as an electrostatic chuck that holds thesubstrate 110 in the process zone 44. The ceiling of the process chamber42 can be flat or rectangular shaped, arcuate, conical, or dome-shaped.Preferably, the ceiling is multi-radius dome-shaped to generate a gooddistribution of plasma source power across the volume of the processzone 44 and to provide a more uniform plasma ion density across thesubstrate surface than a flat ceiling.

The substrate 110 is transferred by a robot arm (not shown) from aload-lock transfer chamber (not shown) through a slit valve (not shown)and into a process zone 44 of the chamber 42. The substrate 110 is heldon the support 46 by an electrostatic chuck and helium is suppliedthrough apertures in the chuck to control the temperature of thesubstrate. Thereafter, the process conditions in the process chamber 42are set to process the etch material 130 of the substrate 110, theprocess conditions comprising one or more of process gas composition andflow rates, power levels of gas energizers, gas pressure, and substratetemperature. The process can also be performed in multiple stages, forexample, each stage having different process conditions. For example, inan etching process, one or more compositions of process gas comprisingetchant gas for etching the substrate 110 are are introduced into thechamber 42. Suitable etchant gases for etching materials on thesubstrate 110 include, for example, chlorine-containing gases andfluorine-containing gases, such as fluorocarbons, and mixtures thereof.The chamber 42 is typically maintained at a pressure ranging from about0.1 to about 400 mTorr. The etchant gas composition is selected toprovide high etch rates and/or high etching selectivity ratios foretching the overlying etch material 130 relative to the underlyingmaterial 122. When multiple layers are being sequentially etched, first,second, third, etchant gas compositions can be sequentially introducedinto the chamber 42 to etch each particular layer.

Process gases, such as the etchant gases, are introduced into theprocess zone 44 of the chamber 42 through a gas distribution system 48that includes a process gas source and a gas flow control system thatcomprises a gas flow control valve. The gas distribution system 48 cancomprise gas outlets 49 located at or around the periphery of thesubstrate 110 (as shown), or a showerhead mounted on the ceiling of thechamber 42 with outlets therein (not shown). Spent process gas andetchant byproducts are exhausted from the process chamber 42 through anexhaust system (typically including a roughing pump and a turbomolecularpump). A throttle valve 54 is provided in the exhaust system 52 tocontrol the flow of spent process gas and the pressure of process gas inthe chamber 42.

A plasma is generated from the process gas using a plasma generator 56that couples an electric field into the process zone 44 of the chamber42, or into a remote zone adjacent to the process chamber 42. The plasmain the process zone 44 is maintained at first process conditionssuitable for etching the etch material 130 of the substrate 110. Asuitable plasma generator 56 comprises an inductor antenna 58 consistingof one or more inductor coils having a circular symmetry with a centralaxis coincident with the longitudinal vertical axis that extends throughthe center of the chamber 42 and is perpendicular to a plane of thesubstrate 110. When the inductor antenna 58 is positioned near the domeceiling, the ceiling of the chamber 42 comprises dielectric material,such as aluminum oxide, which is transparent to RF fields and is also anelectrical insulator material. The frequency of the RF voltage the RFvoltage applied to the inductor antenna 58 is typically from about 50kHz to about 60 MHz, and more typically about 13.56 MHz; and the RFpower level applied to the antenna 58 is from about 100 to about 5000Watts.

In addition to the inductor antenna 58, one or more process electrodes60, 62 can be used to accelerate or energize the plasma ions in thechamber 42. The process electrodes 60, 62 include a ceiling or sidewallsof the chamber 42 that are electrically grounded or biased to serve as afirst electrode 60 that capacitively couples with a second electrode 62below the substrate 110, to form a capacitive electric field thatgenerates or energizes the plasma in the chamber 42. Preferably, thefirst and second electrodes 60, 62 are electrically biased relative toone another by the electrode voltage supply that includes an AC voltagesupply for providing a plasma generating RF voltage to the secondelectrode 62 and a DC voltage supply for providing a chucking voltage tothe electrode 60. The AC voltage supply provides an RF generatingvoltage having one or more frequencies of from about 400 kHz to about13.56 MHz at a power level of from about 50 to about 3000 Watts.

The process chamber 42 further comprises an endpoint detection system 64that operates according to the above-described endpoint detection methodfor detecting an endpoint of a process being performed in the chamber42. Generally, the endpoint detection system 64 comprises a light beamsource 66 adapted to emit the incident light 176, a focusing assembly 68for focusing the incident light 176 onto the substrate 110, and a lightdetector 180 that measures the intensity of the reflected light 178 fromthe substrate 110 to generate the intensity signal 210. A controller 72counts the number of interference fringes in the intensity signal 210.The controller 72 may additionally or alternatively compare portions ofthe real-time measured intensity signal waveform to a storedcharacteristic waveform, or other representative pattern, and adjustprocess conditions in the process chamber 42 when the two waveforms havesubstantially the same shape.

The light source 66 comprises a monochromatic or polychromatic lightsource that generates an incident light 176 having an intensitysufficiently high to provide a reflected light 178 that is reflectedfrom the substrate 110 with a measurable intensity. In one version, thelight source 66 comprises a monochromatic light source that provides aselected wavelength of light, for example, a He—Ne or ND-YAG laser. Inanother version, the light source 66 provides polychromatic light, suchas a xenon or Hg—Cd lamp. Optionally, the polychromatic light source 66can be filtered to provide an incident light 176 having the selectedwavelengths or color filters can be placed in front of the lightdetector 180 to filter out all undesirable wavelengths except thedesired wavelengths of light, prior to measuring the intensity of thereflected light 178 entering the light detector 180. Typically, thelight source 66 may generate a coherent, ultraviolet light. For example,the light source 66 is adapted to generate an emission spectrum of lightin wavelengths of from about 200 to about 800 nm.

One or more convex focusing lenses 74 a, 74 b are used to focus theincident light 176 from the light source 66 as a beam spot 80 onto thesubstrate 110 and to focus the reflected light 178 back on an activelight detecting surface of the light detector 180. The size or area ofthe beam spot 80 should be sufficiently large to compensate forvariations in surface topography of the substrate 110 to enable etchingof high aspect ratio features having small openings, such as vias ordeep and narrow trenches. The area of the reflected light 178 should besufficiently large to activate a large portion of the active lightdetecting surface of the light detector 180. The incident and reflectedlight 176, 178 is directed through a transparent window 82 in theprocess chamber 42 that allows the incident and reflected light 176, 178to pass in and out of the process zone 44.

Optionally, a light beam positioner 84 is used to move the incidentlight 176 across the substrate surface to locate a suitable portion ofthe etch material 130, and optionally also a suitable portion of themask 115, on which to “park” the beam spot 80 to monitor the substrateprocessing. The light beam positioner 84 comprises one or more primarymirrors 86 that rotate at small angles to deflect the incident light 176from the light source 66 onto different positions of the substrate 110(as shown). Additional secondary mirrors can be used (not shown) tointercept the reflected light 178 that is reflected from the substrate110 and focus the reflected light 178 on the light 178 on the lightdetector 180. In another embodiment, the light beam positioner 84 isused to scan the light beam 176 in a raster pattern across the substratesurface. In this version, the light beam positioner 84 comprises ascanning assembly consisting of a movable stage (not shown) upon whichthe light source 66, focusing assembly 68, collecting lens, and detector70 are mounted. The movable stage can be moved through set intervals bya drive mechanism, such as a stepper motor, to move the beam spot 80across the substrate 110.

The light detector 180 comprises a light sensitive electronic component,such as a photomultiplier, photovoltaic cell, photodiode, orphototransistor that provides an electrical intensity signal 210 inresponse to a measured intensity of the reflected light 178 that isreflected from the substrate 110. The intensity signal 210 can be in theform of a change in the level of a current passing through an electricalcomponent or a change in a voltage applied across an electricalcomponent. The reflected light 178 undergoes constructive and/ordestructive interference, which increases or decreases the intensity ofthe reflected light 178, and the light detector 180 provides anelectrical output signal in relation to the measured intensity of thereflected light 178.

The intensity signal 210 generated by the light detector 180 is passedto the controller 72 for evaluation. An illustrative block diagram of anembodiment of the controller 72 and associated computer-readable program320 is shown in FIG. 8. The controller 72 may comprise a plurality ofinterface cards including, for example, analog and digital input andoutput boards, interface boards, such as a hardware interface board 304,and motor controller boards. The controller 72 further comprises acentral processing unit (CPU) 306, such as for example a 68040microprocessor, commercially available from Synergy Microsystems,California, or a Pentium Processor commercially available from IntelCorporation, Santa Clara, Calif., that is coupled to a memory 308 andperipheral computer components. Preferably, the memory 308 includes aremovable storage media 310, such as for example a CD or floppy drive, anon-removable storage media 312, such as for example a hard drive, andrandom access memory 314. The interface between an operator and thecontroller 72 can be, for example, via a display 316 and a light pen318. The light 318. The light pen 318 detects light emitted by thedisplay 316 with a light sensor in the tip of the light pen 318. Toselect a particular screen or function, the operator touches adesignated area of a screen on the display 316 and pushes the button onthe light pen 318. Typically, the area touched changes color, or a newmenu is displayed, confirming communication between the user and thecontroller 72.

In one version, the light wavelength selector 179 comprises software inthe computer-readable program 320 of the controller 72 that is adaptedto select the wavelength of the incident light 176 in order to maximizethe intensity signal 210 of the reflected light 178 at an initial pointof the substrate etching process. For example, the computer-readableprogram 320 may be adapted to drive a stepper motor 94 that is attachedto a component of the light source 66 that changes the wavelength of theincident light 176, the stepper motor 94 being capable of rotating thediffraction grating 92 or prism. Additional light wavelength selectorsoftware of the computer-readable program 320 may be adapted to monitorthe intensity signal 210 of the reflected light 178 and stop thescanning of the wavelength at a local maximum 215 of the intensitysignal 210.

In one embodiment, the light wavelength selector 179 comprises code ofthe computer-readable program 320 that uses the measured thickness ofthe mask 115 to determine the desirable wavelength. For example, thecomputer-readable program 320 may be adapted to determine the localmaximum 215 at which the signal intensity 210 of the reflected light 178reaches a peak. In another example, the controller 72 calculates alinear interpolation of the desirable wavelength based on the known maskthickness and a predetermined proportionality between desirablewavelength and mask thickness. Typically, the relationship between thedesirable wavelength and the thickness is approximately linear, as shownin FIG. 5. Otherwise, the controller 72 may use a non-linearinterpolation to determine the desirable wavelength. Furthermore, boththe local maximum method and the linear interpolation method describedabove may be used together to ensure a more accurate selection of thewavelength.

The computer-readable program 320 of the controller 72 calculates, inreal time, the thickness of the etch material 130 remaining of thesubstrate 110 and accordingly adjusts the process conditions in theprocess chamber 42. The computer-readable program 320 typically countsthe number of interference fringes in the intensity signal 210 of thereflected light 178 and, after a predetermined number of fringes arereached, alters process conditions in the chamber 42 according toprogrammed guidelines. The computer-readable program 320 canalternatively include program code to compare the shape of the intensitysignal 210 to a stored characteristic waveform, or other representativepattern, and determine the endpoint of the etching process when themonitored intensity signal 210 matches the stored characteristicwaveform or pattern.

The computer-readable program 320 may be stored in the memory 308, suchas on the non-removable storage media 312 or on the removable storagemedia 310. The computer-readable program 320 generally comprises processcontrol software comprising program code to operate the chamber 42 andits components, process monitoring software to monitor the processesbeing performed in the chamber 42 safety systems software, and othercontrol software. The computer-readable program 320 may be written inany conventional computer-readable programming language, such as forexample, assembly language, C⁺⁺, Pascal, or Fortran. Suitable programcode is entered into a single file, or multiple files, using aconventional text editor and stored or embodied in computer-usablemedium of the memory 308. If the entered code text is in a high levellanguage, the code is compiled, and the resultant compiler code is thenlinked with an object code of precompiled library routines. To executethe linked, compiled object code, the user invokes the object code,causing the CPU 306 to read and execute the code to perform the tasksidentified in the program.

FIG. 8 also shows an illustrative block diagram of a hierarchicalcontrol structure of a specific embodiment of the computer-readableprogram 320. Using the light pen interface 318, a user may enterinstructions into the computer-readable program 320 in response to menusor screens shown on the display 316. The computer-readable program 320includes program code to control the substrate position, gas flow, gaspressure, temperature, RF power levels, and other parameters parametersof a particular process, as well as code to monitor the chamber process.The process sets are predetermined groups of process parametersnecessary to carry out specified processes. The process parameters areprocess conditions, including without limitations, gas composition, gasflow rates, temperature, pressure and plasma generator settings such asRF or microwave power levels.

The process sequencer instruction set 322 comprises program code toaccept a chamber type and set of process parameters from thecomputer-readable program 320 and to control its operation. Thesequencer program 322 initiates execution of the process set by passingthe particular process parameters to a chamber manager instruction set324 that controls multiple processing tasks in the process chamber 42.Typically, the chamber manager instruction set 324 includes a substratepositioning instruction set 326, a gas flow control instruction set 328,a gas pressure control instruction set 330, a gas energizer controlinstruction set 334, and a process monitoring instruction set 336.Typically, the substrate positioning instruction set 326 comprisesprogram code for controlling chamber components that are used to loadthe substrate 42 onto the support 46, and optionally to lift thesubstrate 110 to a desired height in the chamber 42. The gas flowcontrol instruction set 328 comprises program code for controlling theflow rates of different constituents of the process gas. The gas flowcontrol instruction set 328 controls the open/close position of gas flowcontrol valves (not seen) to obtain the desired gas flow rate. The gaspressure control instruction set 330 comprises program code forcontrolling the pressure in the chamber 42 by regulating the openingsize of the throttle valve 54 in the exhaust system 52 of the chamber42. The gas energizer control instruction set 334 comprises program codefor energizing a gas in the chamber 42. For example, the gas energizercontrol subroutine 334 may comprise code for setting the RF bias voltagepower level applied to process electrodes in the chamber 42. Optionally,a temperature control instruction set may be used to control thetemperature of the chamber components such as sections of the pedestal46.

The process monitoring instruction set 334 comprises code for monitoringa process in the chamber 42. In one version, the process monitoringinstruction set 334 comprises a light detection instruction set 339 tocontrol the light detector 180. For example, the radiation detectioninstruction set 339 may comprise code to set detection parameters of thereflected light 178, such as ranges of wavelengths, or may comprise codeto process a detected signal from the detection means. Additionally, theradiation instruction set 338 may comprise code which determines theendpoint of a process according to a parameter set input by theoperator. For example, the detector 70 delivers a signal related to theintensity of the reflected light 178 to the controller 72. The radiationdetection instruction set 339 contained in the controller 72 may processthe intensity signal 210 corresponding to the reflected light 178 as afunction of time and wavelength. The endpoint of the chamber process maybe determined by the radiation detection instruction set 339 once theradiation signal intensity has reached, for example, a pre-determinedlevel for a certain amount of time. A signal is given by the radiationdetection instruction set 339 to a factory automated host computer 338to halt the chamber process or change the process conditions once theprocess endpoint has been reached.

The data signals received by and/or evaluated by the controller 72 maybe sent to the factory automation host computer 338. The factoryautomation host computer 318 comprises a host software program 340 thatevaluates data from several systems, platforms or chambers, and forbatches of substrates 110 or over an extended period of time, toidentify statistical process control parameters of (i) the processesconducted on the substrates 110 (ii) a property that may vary in astatistical relationship across a single substrate 110 or (iii) aproperty that may vary in a statistical relationship across a batch ofsubstrates 110. The host software program 340 may also use the data forongoing in-situ process evaluations or for the control of other processparameters. A suitable host software program comprises a WORKSTREAMJsoftware program available from aforementioned Applied Materials. Thefactory automation host computer 338 may be further adapted to provideinstruction signals to (i) remove particular substrates 110 from theprocessing sequence, for example, if a substrate property 110 isinadequate or does not fall within a statistically determined range ofvalues, or if a process parameter deviates from an acceptable range;(ii) end processing in a particular chamber 42, or (iii) adjust (iii)adjust process conditions upon a determination of an unsuitable propertyof the substrate 110 or process parameter. The factory automation hostcomputer 338 may also provide the instruction signal at the beginning orend of processing of the substrate 110 in response to evaluation of thedata by the host software program 340.

The present invention is described with reference to certain preferredversions thereof; however, other versions are possible. For example, theendpoint determination method of the present invention can be used todetermine endpoint in deposition, cleaning, or other etching processes,as would be apparent to one of ordinary skill. For example, the methodcan be applied, as would be apparent to one of ordinary skill in theart, to determine endpoint in sputtering etch chambers, cleaningchambers, or deposition chambers. Therefore, the spirit and scope of theappended claims should not be limited to the description of thepreferred versions contained herein.

1. A method of processing a substrate in a process zone, the methodcomprising: (a) determining a reflectance spectrum of light reflectedfrom a substrate, the light having a wavelength; (b) processing thesubstrate by exposing the substrate to an energized gas in the processzone while light having the wavelength is reflected from the substrate;and (c) detecting light having the wavelength after the light isreflected from the substrate, and generating a signal trace of theintensity of the reflected light; and (d) normalizing the signal tracewith the reflectance spectrum of the light and evaluating the normalizedsignal trace to determine an endpoint of the process.
 2. A methodaccording to claim 1 comprising providing a substrate comprising a mask,overlying material on the substrate, or combinations thereof.
 3. Amethod according to claim 1 wherein (a) comprises determining aplurality of reflectance spectrums that are each at a particularwavelength.
 4. A method according to claim 3 wherein (a) comprisesselecting a wavelength of light that provides a local maximum ofintensity from the plurality of reflectance spectrums.
 5. A methodaccording to claim 3 wherein (a) comprises reflecting light that isscanned through a sequence of successive wavelengths and measuring thereflectance spectrum at different wavelengths.
 6. A method according toclaim 5 wherein (a) comprises scanning through wavelengths of from about200 to about 800 nm.
 7. A method according to claim 3 wherein (a)comprises directing a broadband spectrum of light at the substrate, anddetecting a reflectance spectrum of the reflected light at a pluralityof different wavelengths.
 8. A method according to claim 1 wherein thesubstrate comprises a layer, and the method comprises selecting thewavelength of light such that an internal reflection of the light froman interface between the layer and the substrate, and a surfacereflection of the light from the layer, are substantially in phase.
 9. Amethod according to claim 1 wherein the substrate comprises a patternedoverlying material and an underlying material, and wherein (a)comprises, in an initial stage, determining a reflectance spectrum ofthe underlying material of the substrate when it is substantially absentthe patterned overlying material; and wherein (d) comprises normalizingthe signal trace of the detected light that is reflected from thesubstrate by the intensity of the reflectance spectrum of the underlyingmaterial of the substrate.
 10. A method according to claim 1 wherein thesubstrate comprises a layer, and further comprising selecting awavelength of light at which the layer is substantially permeable tolight having the wavelength.
 11. A method according to claim 1comprising providing a substrate comprising a mask, and wherein in (a),a first portion of light having the wavelength is reflected from thesurface of the mask and another portion of the light passes through themask and is reflected from the interface between the mask and thesubstrate, and the wavelength is the wavelength of light at which theinterface and surface reflections of light are substantially in phaseupon emerging from the substrate.
 12. A method according to claim 1wherein the substrate comprises polysilicon exposed between features ofa nitride mask, wherein (b) comprises providing an energized gas capableof etching the polysilicon, and wherein in (a) the wavelength of thelight is from about 200 to about 800 nm.
 13. A method of processing asubstrate in a process zone, the substrate comprising an overlyingmaterial and an underlying material below the overlying material, themethod comprising: (a) determining a reflectance spectrum of lightreflected from the underlying material of the substrate when it issubstantially absent the patterned overlying material; (b) processingthe substrate having the overlying material and the underlying material,by exposing the substrate to an energized gas in the process zone whilelight having the wavelength is reflected from the substrate; and (c)detecting light having the wavelength after the light is reflected fromthe substrate, and generating a signal trace of the intensity of thereflected light; (d) normalizing the signal trace with the reflectancespectrum of the light from the underlying material; and (e) evaluatingthe normalized signal trace to determine an endpoint of the process. 14.A method according to claim 13 wherein (a) comprises selecting thewavelength of the light such that light having the wavelength provides alocal maximum of intensity from the overlying material.
 15. A methodaccording to claim 14 wherein (a) comprises reflecting light that isscanned through a sequence of successive wavelengths and measuring thereflectance spectrum at different wavelengths.
 16. A method according toclaim 15 wherein (a) comprises scanning through wavelengths of fromabout 200 to about 800 nm.
 17. A method according to claim 14 wherein(a) comprises directing a broadband spectrum of light at the substrate,and detecting a reflectance spectrum of the reflected light at aplurality of different wavelengths.
 18. A method according to claim 14comprising selecting the wavelength of light such that an internalreflection of the light from an interface between the overlying materialand the substrate, and a surface reflection of the light from theoverlying material, are substantially in phase.
 19. A method accordingto claim 14 wherein the substrate comprises a patterned overlyingmaterial.
 20. A method according to claim 13 wherein the substratecomprises polysilicon exposed between features of a nitride mask,wherein (b) comprises providing an energized gas capable of etching thepolysilicon, and wherein in (a) the wavelength of the light is fromabout 200 to about 800 nm.